JPH0736605B2 - Electrophotography - Google Patents

Description

The present invention relates to an electrophotographic method in which band-like fog in the main scanning direction is suppressed and the reproducibility of fine lines such as one dot line in the sub scanning direction is improved.

[Conventional technology]

An electrophotographic apparatus using a light beam (a type that exposes a background portion; the same applies hereinafter) includes, for example, one shown in FIG. In this electrophotographic apparatus, a light beam 2 of a laser beam 1 is modulated by a modulator 3 according to an image signal, a modulated light beam 4 is deflected in a main scanning direction by a rotary polygon mirror 5, and is rotated via a lens diameter 6. The photosensitive member 7 is exposed.
By this exposure, an electrostatic latent image is formed on the photoconductor 7 and transferred to the recording paper 8 after development.

Figure 5 shows the energy density ratio of a light beam for exposing the photosensitive member 7, the maximum value on each scan line S _1, S _2, S _3, the intermediate of the scan lines S _1, S _2, S ₃ It has the shape of a Gaussian distribution becomes 1 / e ² of the maximum value at point position G _1, G _2. Since the diameter d of the light beam is defined to be determined by the point where the light intensity becomes 1 / e ^{2 of the} center of the light beam, the scanning lines S ₁ , S
The ratio k between the distance P between ₂ and S ₃ and the diameter of the light beam is k = d / P = 1 in the case of FIG. In the figure, B ₁ indicates the energy density ratio of a single light beam, and B ₂ indicates the combined energy density ratio.

When the photoconductor 7 is exposed by the light beam 4 which is modulated according to the image signal, the area corresponding to the background portion is exposed by the light beam having the energy pattern of the curve B ₂ and thus in the main scanning direction. Generates a running belt-shaped fog.

The scanning line interval P is, for example, 64 μ for a laser printer having a resolution of 400 SPI and 32 μ for a laser printer having a resolution of 800 SPI. Therefore, in the electric field that directly affects the development, this uneven exposure is emphasized.

It is conceivable to increase the developing bias voltage to suppress this band fog, but if the bias voltage is increased enough to eliminate band fog, the potential contrast in the image area will be insufficient, and even the carrier in the developer will be transferred to the photoconductor. Inconvenience such as adhesion occurs.

An electrophotographic method disclosed in Japanese Patent Application Laid-Open No. 58-152269 has been proposed as a method for suppressing band-shaped fogging without such inconvenience. According to this electrophotographic method, if the diameter d of the light beam and the scanning line interval P are set so that the ratio becomes 1.3 ≦ k = d / P ≦ 1.9, the band-shaped fog described above can be suppressed. There is.

[Problems to be solved by the invention]

However, according to the conventional electrophotographic method, the band-shaped fog is suppressed by optimizing the beam diameter. Therefore, when the beam diameter is increased to suppress the band-shaped fog, one dot line or the like in the sub-scanning direction is generated. Reproducibility of fine lines may be reduced.

[Means and Actions for Solving Problems]

The present invention has been made in view of the above, and in order to improve the reproducibility of a fine line in the sub-scanning direction while suppressing the band-shaped fog running in the main scanning direction, the photo-electrification curve of the photoconductor is approximated by two straight lines. , When the exposure energy corresponding to the intersection of this straight line is used as the reference exposure energy, an electrophotographic method is provided in which the background portion is illuminated with a light beam having an energy in the range of 1.1 to 1.4 times the reference exposure energy. To do.

〔Example〕

 Hereinafter, the electrophotographic method according to the present invention will be described in detail.

[A] Prevention of band-shaped fogging (1) Quantum efficiency of carrier light generation of photoconductor η η = η ₀ × (E / E ₀ ) ⁿ (1) where η ₀ : at a certain electric field E ₀ Quantum efficiency E: Internal electric field of photoconductor n: Constant indicating the electric field dependence of quantum efficiency. For example, in the case of the _Se -organic composite photosensitive material, n = 1/2, and in the α- _Si photosensitive material, n = 0. (2) Photostatic property of photoconductor When the relationship of the formula (1) is satisfied, The static elimination characteristics are expressed as follows.

V ^(1-n) = V ₀ ^(1-n) -S × I (2) where V ₀ : initial potential of the photosensitive member S: sensitivity constant of the photosensitive member I: exposure energy (3) of the photosensitive member as a characteristic matter photoreceptor of the optical charge removing properties, S _e - with organic composite sensitive material, (2)
The formula is n = 1/2, Becomes Here, the exposure energy I was changed and the potential V based on the photo-electrification characteristics of the photoconductor was measured. The measurement results are shown in FIG. The horizontal axis represents the ratio of the exposure energy when the exposure energy at the intersection X of two straight lines L ₁ and L ₂ described later is the reference light amount (1.0), and the vertical axis represents the potential V of 1 /. It is shown after being converted to the square (the vertical axis is (1-
n) is the power axis, and if n = 1/2, it becomes the power axis 1/2).

As is clear from FIG. 1, if the horizontal axis indicates the exposure energy I on the horizontal axis and the vertical axis indicates the photoconductor potential V as the (1-n) th power axis, the photo-electrification characteristics are two straight lines L ₁ , L ₂ is approximately expressed as a characteristic item. The straight line L ₂ has a smaller inclination than the straight line L ₁ and corresponds to the residual potential portion.

(4) Modeling of Photo-Electrification Property of Photoreceptor Considering the above-mentioned residual potential portion, the equation (3) can be modeled as follows.

(4.1) Area a (area below the reference light intensity) In the model formula of, if n = 1/2, (4.2) Area b (area below the standard light intensity) In the model formula of, if n = 1/2, Here, V: photoconductor potential after exposure energy I is given C _ER : ratio of inclinations of _two straight lines L ₁ and L ₂ VR: potential of intersection X (generally called residual potential) (5) Sub Potential unevenness in the scanning direction ΔV ΔV = V _max -V _min (5) where V _{max is} the maximum value of the photoconductor potential V when the minimum value I _min of the exposure energy I is given V _min : the exposure energy The minimum value of the photoconductor potential V when the maximum value I _max of I is given. (6) Light amount unevenness ΔI in the sub-scanning direction The above-mentioned potential unevenness ΔV of (5) is caused by the following light amount unevenness ΔI. .

Here, k _p = d _p / P, and d _p : light beam diameter in the sub-scanning direction P: scanning line interval According to the measurement results shown in FIG. 1, V ₀ = 8000 [V], VR
= 200 [V] and C _ER = 0.3 were obtained.

Now, with k _p = d _p /P=1.6, (4.1), (4.2),
By using the equations (5) and (6), the relationship between the exposure energy I = (I _min + I _max ) / 2 and the potential unevenness ΔV can be obtained. The calculation result is shown in FIG.

Here, as a concept for suppressing the band-shaped fog running in the main scanning direction, “even if the exposure unevenness ΔI exists, the potential unevenness ΔI
V is difficult to output. As a condition therefor, at "normal bias voltage set value V _B = background portion potential + 100 [V]", potential unevenness ΔV is ± 15 [V] (contrast 30
[V]) Must be below. ]

From FIG. 2, the exposure energy I must be 1.1 times or more of the reference exposure energy in order to satisfy this condition.

Similar investigations were made using other sensitive materials, for example, α-S _i sensitive material, but similar results were obtained.

[B] Reproducibility of fine line such as 1-dot line In order to understand the relationship between reproducibility of 1-dot line and beam diameter, the present inventor first carried out simulation calculation by developing electric field analysis. The values (sensitive material, exposure energy) used for the calculation are the same as the values of [A] described above. As a result, the range of exposure energy that can reproduce a good one-dot line is 1 ≦ 1.4 × (reference exposure energy), and the line width W reproduced is stable at W / p 0.86 to 0.88 with respect to the scan hitch p. The value itself was not a problem. On the contrary, it was found that when 1> 1.4 × (reference exposure energy), the density of the edge portion of the fine line was lowered, and the adhesion of a thin toner layer generally called scattered toner occurred near the edge portion. (A) and (b) in FIG. 3 show this, In (b), it is 1.6.
In (b), scattered toner t is seen.

From the above analysis results, the inventor determined that the optimum light amount range Got

[C] Experimental Verification Results The inventor verified the above analysis results by experiments. The experimental machine used has a beam expander in both main and sub directions, and the beam diameter in both main and sub directions can be changed independently.
It is a laser printer with a laser scanning optical diameter that can change the writing resolution from 400 to 1400 SPI. The experiment
It was done at 800 SPI. First, the occurrence of band-like fogging in the background was examined at d / p = 1.6. As a result, development bias =
By setting the background potential +100 [V], Then, it was confirmed that no band-shaped fogging occurred.

Next, I investigated the reproduction of one dot line, In the case of 1 dot line in either the main scanning direction or the sub scanning direction, W / p 0.94 to 0.98 and stable and good fine line reproducibility were obtained. The W / P was larger than the analysis result because the line width was thickened due to the fixation, which was a favorable result.

vice versa, Then, even though the line width was not changed for both one-dot lines in the main / sub amount direction, the reproduction of the edge portion of the fine line was poor, especially in the line running in the sub-scanning direction.

The quality of both reproduction lines became clearer when comparing the samples copied by a normal copying machine with the print sample as the original.

〔The invention's effect〕

As described above, according to the electrophotographic method of the present invention, when the photo-electrification curve of the photoconductor is approximated by two straight lines and the exposure energy corresponding to the intersection of these straight lines is used as the reference exposure energy, this reference exposure Since the background portion is irradiated with the light beam having the energy in the range of 1.1 to 1.4 times the energy, the reproducibility of the fine line in the sub-scanning direction can be improved while suppressing the band-shaped fog running in the main scanning direction.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the photo-electrification characteristics of the photoconductor. FIG. 2 is an explanatory diagram showing potential unevenness on the photoconductor. Figure 3 (a), (b)
3A and 3B show the reproducibility of a fine line in the sub-scanning direction, (A) is according to the present invention, and (B) is an explanatory view showing something outside the scope of the present invention. FIG. 4 is an explanatory view showing a conventional laser printer.
FIG. 5 is an explanatory diagram showing exposure energy of a Gaussian distribution light beam. Explanation of symbols V ... Photoconductor potential I ... Exposure energy ΔV ... Photoconductor potential unevenness

Claims (1)

[Claims] 1. An electrophotographic method for forming an electrostatic latent image by exposing a background portion of a uniformly charged photoconductor with a light beam according to an image signal to increase the amount of energy for exposing the photoconductor. The photo-static property obtained by measuring the decrease in the potential of the photoconductor with respect to is approximated by two straight lines with different drop rates, and the exposure energy at the change point of the drop rate is used as the reference exposure energy. It is characterized in that the background portion is irradiated with a light beam having an intensity such that the average value of the maximum value and the minimum value of the exposure energy when exposing a part is 1.1 times to 1.4 times the exposure energy of the reference exposure energy. Electrophotography.